Mechanistic insights into growth stage–associated saline–alkali stress alleviation in wetlands: Na⁺/K⁺ gradient patterns and rhizosphere bacterial adaptive responses

Soil salinization is a key stressor constraining wetland ecosystem functioning, while excessive Na⁺ accumulation, Na⁺/K⁺ imbalance, and sodicity risk can induce ionic toxicity and osmotic stress. Salt-tolerant plants alleviate soil saline-alkali stress by regulating ion homeostasis and rhizosphere interactions. However, whether stage-associated rhizosphere bacterial restructuring is linked to plant Na⁺/K⁺ patterns remains unclear. This study focused on typical saline-alkali wetlands in the Xianghai-Momoge region of the Songnen Plain. Field sampling was conducted at the rapid growth, mature, and senescence stages, and in situ simulation experiments were performed. We examined hydro-soil saline-alkali conditions, Na⁺/K⁺ gradient changes, and rhizosphere bacterial succession. The results indicated a potential salinity-mitigation window at the mature stage. Na⁺/K⁺ decreased by up to 89.7% in water, 64.2% in soil, and 29.2% in roots. Rhizosphere bacterial communities also showed stage-associated restructuring. Bacterial richness decreased significantly at mature stage, mainly reflected by lower ACE and Chao1 indices. PICRUSt2 functional prediction showed that the predicted abundances of Na⁺ efflux-related KOs, nhaA and nhaB, at the mature stage were approximately 3.1- and 5.1-fold higher than those at the rapid growth stage, respectively. K⁺ uptake-related KOs, trkH and kdpA/kdpB, also showed higher predicted abundances. Procrustes analysis indicated concordance between soil sodicity restructuring and rhizosphere microbial community shifts. Therefore, maturity represents a key stage when saline-alkali stress mitigation and rhizosphere bacterial restructuring coincide, while sodicity rebound risks should be monitored during senescence. This study provides a basis for stage-specific restoration assessment and environmental safety management in inland saline-alkali wetlands.